The photoreceptor cells (rods and cones) in the albino rat retina degenerate with age; exposure to light equal to or greater than 300 foot-candles accelerates this process. Preliminary data indicate that hormones influence photoreceptor cell degeneration: hypophysectomy and gonadectomy both protect against the damaging effects of visable light, whereas high plasma levels of prolactin accentuate cell destruction. Preliminary data indicate that chronic stress for 8 hours/day for 7 days (but not 4 hours/day for 7 days) also affects photoreceptor cells in rats. In another pilot study, chronic stress 4 hours/day for 1 year (between 12 and 24 months of age) totally abolished the retinal photoreceptor cells and badly damaged the bipolar cells. The investigator plans to examine the retinas of animals from all projects in the program. He will perform light and EM microscopy to determine the morphological extent and localization of damage to retinal neurons induced by age, stress, or change in hormonal state. The specific aims are to correlate the type and duration of stress for different ages to the severity of retinal damage; to correlate the aging and stress-induced endocrine changes with retinal damage; and to determine periods of vulnerability to chronic stress during aging.